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Axial myopia

Axial myopia is myopia caused by anteroposterior elongation of the globe for its optical power, placing the focal point in front of the retina. Often imaged on CT or MRI when evaluating refractive error, high myopia complications, or orbital pathology in symptomatic patients.

Key Images

Axial Myopia

Emmetropia: Completely normal, and it means the globe size is perfectly proportional.

Look For First
  • AP-predominant globe elongation along the visual axis rather than uniform enlargement
  • Smooth posterior pole without focal outpouching in uncomplicated cases
  • Bilateral and often symmetric or asymmetric axial length increase without intraocular mass or abnormal enhancement
Key Image Findings
  • The globe is elongated primarily along the anteroposterior (visual) axis with relatively preserved lens and anterior segment, distinguishing it from diffuse globe enlargement.
  • On CT, axial myopia appears as AP-predominant globe elongation generally without an intraocular mass; MRI better assesses the posterior globe, retina/choroid, optic nerve, and associated soft-tissue findings.
  • In uncomplicated axial myopia, the posterior globe may be smoothly elongated without focal posterior bulging, whereas posterior staphyloma is a localized outpouching of thinned sclera/uvea with more pronounced curvature than the adjacent globe wall.
  • Posterior staphyloma typically involves the posterior pole in peripapillary or temporal distribution; CT shows the focal posterior bulge and scleral-uveal rim thinning.
  • High myopia is often defined as refractive error of −6 diopters or more, with axial lengths typically greater than 26–26.5 mm, though thresholds vary.
  • Associated findings in pathologic myopia include myopic maculopathy, chorioretinal atrophy, lacquer cracks, myopic choroidal neovascularization, myopic traction maculopathy/foveoschisis, and retinal detachment.
  • High myopia increases risk for glaucoma and cataract but is not synonymous with pathologic myopia; pathologic myopia requires characteristic posterior-pole disease (maculopathy and/or staphyloma) in addition to excessive axial length.
  • Uncomplicated axial myopia should lack focal posterior staphyloma, intraocular mass, abnormal enhancement, calcification, hemorrhage, retinal detachment, or abnormal vitreous signal.
Etiology

Axial myopia occurs when the eye grows too long from front to back relative to the focusing power of its cornea and lens. In most people, there is no single cause: inherited susceptibility and visual environment interact during childhood eye growth. NCBI Bookshelf; EyeWiki

Common contributors

  • Genetics: Myopia in one or both parents increases a child’s likelihood of developing it. EyeWiki; Cleveland Clinic
  • Less time outdoors: Lower outdoor exposure in childhood is associated with greater risk of myopia. Cleveland Clinic; All About Vision
  • Sustained near work: Reading, studying, and other prolonged close-up tasks are associated with myopia development or progression. Screen use is one form of near work rather than a unique cause. Cleveland Clinic; PubMed Central
  • Altered eye-growth signaling: During normal development, retinal visual feedback helps match axial length to the eye’s optics. Disruption of that process can promote axial elongation, with remodeling and thinning of the posterior sclera. NCBI Bookshelf; PubMed Central

Less common causes

Axial elongation can also occur with congenital glaucoma, retinopathy of prematurity, posterior staphyloma, or after scleral buckle surgery. Early visual deprivation—for example, an untreated dense congenital cataract or severe ptosis—can contribute as well.

These are distinct from refractive causes of myopia, such as a nuclear sclerotic cataract, which changes optical power without necessarily lengthening the eye. EyeWiki

Differential Diagnosis
  • Buphthalmos: diffuse enlargement of entire globe including anterior and posterior segments due to elevated intraocular pressure in congenital or infantile glaucoma, unlike the AP-predominant elongation of axial myopia.
  • Posterior staphyloma: focal posterior outpouching superimposed on an elongated myopic globe, in contrast to simple axial myopia which has smooth AP elongation without a distinct focal bulge.
  • Coloboma: congenital focal wall defect or outpouching classically in the inferonasa location, may coexist with other congenital ocular abnormalities and should be distinguished from myopic staphyloma.
  • Intraocular mass: abnormal enhancement, calcification, hemorrhage, or abnormal vitreous signal should not be attributed to uncomplicated axial myopia and must be excluded on imaging.
Discussion

Axial myopia is distinguished by elongation along the visual axis with preserved anterior segment anatomy, whereas buphthalmos reflects diffuse glaucomatous enlargement in pediatric patients.

Posterior staphyloma represents advanced pathologic myopia with focal scleral thinning and outpouching, often at the posterior pole; its presence indicates increased risk for retinal complications and vision-threatening disease.

High myopia (≥−6 diopters or axial length >26–26.5 mm) does not equal pathologic myopia; the latter requires both excessive axial length and characteristic posterior-segment disease such as maculopathy or staphyloma.

MRI is superior to CT for assessing posterior globe, retina/choroid, optic nerve, and soft-tissue complications in axial myopia, while CT clearly shows the focal scleral bulge and rim thinning of staphyloma.

Progressive axial elongation carries increased risk for glaucoma, cataract, myopic maculopathy, chorioretinal atrophy, lacquer cracks, myopic choroidal neovascularization, traction maculopathy/foveoschisis, and retinal detachment.

Accurate terminology in reporting—'axial elongation of the globe due to high myopia' rather than vague terms—improves communication with ophthalmology and guides clinical management and monitoring.

Reporting Pearls

Use clear, specific terminology: describe "bilateral (or asymmetric) AP elongation of the globes compatible with axial myopia" for uncomplicated cases, and add "focal posterior scleral/uveal outpouching consistent with posterior staphyloma" when present; explicitly exclude intraocular mass, abnormal enhancement, and retinal detachment to distinguish from pathologic complications.

Pitfalls
  • Confusing axial myopia with buphthalmos: buphthalmos shows diffuse globe enlargement including the anterior segment due to childhood glaucoma, whereas axial myopia has AP-predominant elongation with preserved anterior segment.
  • Overlooking or minimizing a focal posterior staphyloma by dismissing it as simple elongation; staphyloma is a distinct focal outpouching with thinned sclera/uvea and indicates advanced pathologic myopia with higher complication risk.
  • Attributing intraocular complications (retinal detachment, hemorrhage, abnormal enhancement, calcification) to uncomplicated axial myopia rather than investigating them as separate pathology.
  • Using imprecise terminology such as 'macrophthalmos' alone without specifying the mechanism (axial elongation, buphthalmos, or staphyloma), which can obscure the clinical diagnosis and confuse ophthalmologic interpretation.
Source: Reference source